I'm currently a lvl 8 Khajiit I have perks in stealth 1/5, backstab, deadly aim, overdraw 1/5, and armsman 1/5. I have two perks I havn't used yet and before I do I wanted to see what other assassin/thieves were focusing on as far as perks go.

assassins blade + silence = backstabbing galore.

^this

For the beginning, I would recommend the following priority:

1. Stealth
2. Weapon type of your choice
3. some magic/armor or 2nd weapon type

Reason: To really achieve anything you depend on not being seen. You can't deal damage as a warrior would, but you will rock the world while in stealth. To avoid being totally screwed when detected, you still should be able to deal some decent damage (also you want to make sure to 1hit-kill while in stealth mode). The third priority depends on your playstyle.

For me this is stealth, one-handed and light armor/illusion.

Invest in alchemy.

I heavily recommend getting to at least 4/5 stealth, backstab, the one where your speed doesn't matter, and trying to get a pair of gloves with "backstab does double damage"
The rolling ability is nice too for getting out of the light quickly
Hope that helps!

daggers can become insanly powerful with the right perks. my backstabbing multiplikator is at 30 now. using a superior elven dagger with 16 damage, I get 480 backstab damage. to balance things out I'm always running around in brotherhood armor, which keeps me weak in direct confrontations so I'm forced to use alchemy or run for cover.

Make sure to keep your one handed and archery leveled and the perks so they can be strong enough to one hit. At higher sneak levels I find that firing arrows from the shadows works well as they will stay in caution and lose interest quickly. Also, if caught just push the enemy back and run and hide in the shadows. Usually they'll lose you and you can get more attacks in.

And if you're doing a stealthy character build keep in mind that sneaking all the time will inadvertently grind up your sneaking. pickpocketing, lock picking, etc. skills will your more offensive ones take longer. In a open fight against tough heavy armored boss enemies you'll be rocked hard, but in sneak mode you could easily thrash everything in the dungeon.
I wish sneak of 100 still gave you the ability to ignore enemy armor and hit the health directly like in Oblivion.

So do Armsman, Dual Flurry, Dual Savagery perks all affect daggers?
I think i saw someone say Armsman for example does not affect daggers...

Stealth and archery. Enjoy killing bosses with sneak attacks without them having a chance of fighting back.

assassins blade is a must!

Can someone please answer my question?

Yep, seems we play exactly the same type of character .

Please explain how the hell you have x30 backstab?

assassins blade gives me 15x backstab, wearing dark brotherhood gloves doubles it.